The invention relates to a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles.
In heavy commercial vehicles, the parking brake is actuated by what are known as spring force accumulator cylinders (spring-loaded cylinders). Here, the brake actuating force is generated via a spring force, with the result that the requirements for a mechanically actuated parking brake are satisfied.
Since the spring force accumulator cylinders are, as a rule, designed to generate very high forces, manual release of the parking brake in the operating case is not appropriate. In the case of pneumatically actuated brakes, the release therefore takes place by means of compressed air.
In order to make this possible, spring force accumulator cylinders are, as a rule, equipped with a release piston. It is possible by way of this piston, if compressed air is introduced, to compress the spring to such an extent that the brake is released. In order that the parking brake is not engaged while driving, the piston is loaded constantly with compressed air, with the result that the spring cannot be relieved and therefore the parking brake does not start to act.
A common design is what is known as a combined cylinder. This cylinder includes or combines two different brake cylinder types, namely a spring force accumulator cylinder for the parking brake system (PBS) and a compressed air cylinder (usually a diaphragm cylinder) for the service brake system (SBS).
The two cylinders are usually arranged behind one another in an axial direction. The spring force accumulator part, which acts with its piston rod on the piston collar of the diaphragm cylinder and by the latter, in turn, on the brake lever, is arranged behind the diaphragm part of the combined cylinder.
This design requires a relatively large amount of installation space. However, the installation space is being limited increasingly by the introduction of more complex chassis systems, such as independent suspension systems, lightweight axles, etc.
There are therefore efforts to minimize the space requirement for the parking brake cylinder by other designs and methods of operation. To this extent, what is known as a compact combined cylinder affords a compact design. DE 10 2005 044 708 A1 (corresponding to U.S. Pat. No. 7,523,999 B2) discloses a brake cylinder of this type. In DE '708, the function of the parking brake cylinder is integrated directly into the service brake cylinder. Here, the spring force accumulator spring is no longer actuated via a separate spring force accumulator piston, but rather likewise via the piston of the service brake cylinder. In order to release the parking brake, the SBS piston is loaded for a short time period by way of a special actuation with compressed air. As described, the parking brake is released as a rule with the aid of compressed air.
In the compact combined cylinder which is known from the above-mentioned DE 10 2005 044 708 A1, the pressure supply of the locking mechanism takes place by way of a centrally arranged, stationary supply tube which is guided through the axially movable piston. Since the spaces which are formed by the piston have to be closed in an airtight manner with respect to one another, the piston is correspondingly sealed with respect to the supply tube by use of a sliding seal. However, this sliding seal is subjected to very pronounced wear, since a large sliding travel in comparison with the seal of relatively low dimensions has to be covered during every brake actuation.
Naturally, this represents an extremely unsatisfactory solution, which not only leads to an impairment of the functional reliability of the parking brake, but is also associated with considerable costs, in particular as a result of repair work.
The invention is based on the object of developing a brake cylinder of the generic type in such a way that an improvement in the functional reliability and a longer service life are achieved with structurally low complexity.
This object is achieved by a brake cylinder for a pneumatically actuable vehicle brake, in particular for a commercial vehicle, including a spring force accumulator brake section for carrying out parking brake operations by way of a spring force accumulator spring, and a service brake section for carrying out service brake operations, which are actuated by compressed air. The spring force accumulator brake section and the service brake section are combined in a housing to form one structural unit. The housing is divided by a piston into a pressure space loadable with compressed air and a further space. The pressure space serves for actuating the service brake section, and the spring force accumulator spring of the spring force accumulator section is arranged in the further space on the opposite side of the piston. The spring force accumulator spring acts in the space on a further spring force accumulator piston, which can be locked with respect to the piston by a pneumatically actuable locking mechanism and can be released by release of the locking mechanism. The accumulator piston is connected directly or via further elements to a piston rod for actuating the vehicle brake. Compressed air is fed to the locking mechanism via a compressed air hose.
The use of a sliding seal can be dispensed with as a result of this structural refinement of the brake cylinder. This results in a significant increase in the service life of the brake cylinder, since the feed region of the compressed air to the locking mechanism no longer has to be sealed to the previously required extent. In principle, one sealing ring is sufficient to seal the line, which is guided through the piston but is rigidly connected to the piston. The functional capability of the brake cylinder, in relation to this pass-through region, therefore remains independent of the number of brake actuations.
There is provision according to one advantageous embodiment of the invention to guide the hose connections laterally, preferably tangentially, both on the cylinder housing and on a cover which is connected to it and on the piston. As a result, the movement of the piston can take place without impairment. A further contribution is made to this by the fact that the compressed air hose is laid approximately annularly, in the nonfunctional position of the piston in a pressure space which is formed. The hose connections are preferably configured as angled parts.
Further advantageous embodiments of the invention are described herein.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.